Currently aviation has one aeronautically protected frequency available to support Safety of Life operations. As the GPS constellation evolves it will provide a second signal (L5) which will provide more robustness. As GLONASS fulfils its Standards and Recommended Practices (SARPS) as detailed in ICAO Annex 10 and Galileo and Beidou become operational, there will be multiple frequencies and alternative constellations available. This will further improve GNSS robustness and may enable ATM consider rationalisation of some ground-based navigation aids as contingency measures will be less likely.
ICAO has developed a GNSS Concept of Operations (CONOPS) addressing future space-based infrastructure and this CONOPS focuses on a Dual Frequency - Multi Constellation (DF-MC) environment.
